Patients may also have studies to measure levels of Rolipram in the blood. These are done on study days 1 and 29 and at months 2, 4, and 6. For days 1 and 29, a catheter is placed in an arm vein and 4 ml. of blood is drawn immediately before the morning dose and at several intervals from 20 minutes to 6 hours after the dose. For the other tests, a single 4-ml sample is collected before the noon dose.